ISO 4217 is an international standard describing three letter codes to define the names of currencies established by the International Organization for Standardization, ISO. This eliminates the problem caused by the names Dollar, Franc and Pound being used in dozens of different countries, all with wildly differing values. The standard also defines the relationship between the Major currency unit, and any Minor currency unit. Often the Minor currency unit has a value that is 1/100 of the Major unit. However, there are some countries that have a Minor currency unit that is 1/10, 1/20 or even 1/5 of the Major currency unit. A few countries do not have a Minor currency unit at all. The first two letters of the code are the 2 letters of ISO 3166-1 alpha-2country codes.

ISO 4217 includes codes for not only currencies, but also codes for precious metals (gold, silver, palladium and platinum; normally measured in troy ounces) and certain other entities used in international finance, e.g. Special Drawing Rights. There are also special codes allocated for testing purposes (XTS), and to indicate no currency transactions (XXX). These codes all begin with the letter "X".

Over time, new currencies are created and old currencies are discontinued. As a result, the list of codes must be updated from time to time. The ISO 4217 maintenance agency (MA), the British Standards Institution[?], is responsible for maintaining the list of codes.